Contact lenses have been used commercially to improve vision since at least the 1950s. The first contact lenses were made of hard materials and as such were somewhat uncomfortable to users. Modern soft contact lenses are made of softer materials, typically hydrogels. Recently soft contact lenses made from silicone hydrogels have been introduced. Silicone hydrogels are water-swollen polymer networks that have high oxygen permeability. However, some users experience discomfort and excessive ocular deposits leading to reduced visual acuity when using these lenses.
Others have tried to alleviate this problem by coating the surface of silicone hydrogel contact lenses with hydrophilic coatings, such as plasma coatings. For example, it has been disclosed that silicone hydrogel lenses can be made more compatible with ocular surfaces by applying plasma coatings to the lens surface or by treating the surface with reactive hydrophilic polymers. Reactive functionalities on or near the surface of medical devices are chemically attached to reactive functional groups on a hydrophilic polymer, thereby creating a hydrophilic surface. In one example, Vinylpyrrolidone-co-4-vinylcyclohexyl-1,2-epoxide polymer was used to coat a silicone substrate. However, surface modifications are usually added steps in contact lens production.
Surface active macromonomers comprising 10-90% repeating units from ethylenically unsaturated hydrophobic monomer have been disclosed for use in contact lens applications. A 2-step reaction is carried out to form a PVP-methacrylate. The total process involves several synthetic steps and, as a result, requires extensive purification of each intermediate. The resultant “surface-active macromonomers” are low in molecular weight with Mn, Mw, and polydispersity values of 4,900, 8,900, and 1.8, respectively (versus PEG standards). The inclusion of substantial quantities of hydrophobic monomers may prevent the formation of wettable contact lenses. Wettability data for lens wear longer than one hour is not reported.
Incorporation of internal hydrophilic wetting agents into a macromer containing reaction mixture has been disclosed. However, not all silicone containing macromers display compatibility with hydrophilic polymers. Modifying the surface of a polymeric article by adding polymerizable surfactants to a monomer mix used to form the article has also been disclosed. However, lasting in vivo improvements in wettability and reductions in surface deposits are not likely.
Poly(N-vinyl-2-pyrrolidone) (PVP) or poly-2-ethyl-2-oxazoline have been added to hydrogel compositions to form interpenetrating networks which show a low degree of surface friction, a low dehydration rate and a high degree of biodeposit resistance.
It has been previously shown that high molecular weight (Mw>300,000) PVP can be entrapped within a cross-linked silicone hydrogel matrix. However, a small loss of the high molecular weight PVP (<10 weight percent) is still observed during the extraction purification process in organic solvents.
Therefore it would be advantageous to find additional hydrophilic polymers which may be incorporated into a lens formulation to improve wettability of the lens without a surface treatment.